Magnetic resonance imaging (MRI) is a state of the art imaging technology which allows cross sectional viewing of objects like a human body with unprecedented tissue contrast. MRI is based on the principles of nuclear magnetic resonance (NMR), a spectroscopic technique used by scientists to obtain microscopic chemical and physical information about molecules. The basis of both NMR and MRI is the fact, that atomic nuclei with non-zero spin have a magnetic moment. In medical imaging it is usually nuclei of hydrogen atoms (i.e. protons 1H) which are studied since they are present in the body in high concentrations like for example as water. Radio frequency waves are directed at the nuclei in strong external magnetic fields, which lead to an excitation of the protons and a relaxing of the protons. Due to the relaxation of the protons, radio signals are emitted which can be detected and computer processed to form an image. Magnetic resonance (MR) radio frequency (RF) receive coils are necessary parts to receive said RF signals transmitted in a particular MR experiment. The best antenna element location is close to the human body being scanned and therefore most of the MR receive coils are positioned on the patient by a scanner operator.
Since MR receive coils or in general MR receive chains comprising the coils and various electronic components like amplifiers, switches etc, are highly sensitive to disturbances by external radio frequency waves, said MR receive chains have to be electromagnetically shielded which requires the spatial separation of the MR receive chains in an examination room and the control system in a separate technical room.
Current state of the art MR receive chains feature a massive parallel analogue solution with many expensive analogue design elements such as RF switches, RF amplifiers, RF power supplies, RF cables and RF connectors etc. All these components are typically strewn over a distance of 10-20 meters between the receive chain in the exam room and the analogue to digital converters in a technical room, which makes it one of the most complex and challenging aspects to cost effectively design and produce an MR scanner due to component spread and unwanted interactions between the many galvanic parts.
These problems become even more severe in the case of higher element counts in coils, i.e. coil systems comprising multiple individual coils which need to be effectively combined using a state of the art wire technology. Also, in MRI systems each galvanic wire needs draping considerations and careful design to avoid image quality detrimental effects due to galvanic wiring coupling effects.
Also, the actual workflow effectiveness of a particular coil implementation is very important to the MR scanner's operation since it determines in a large part the patient throughput of the MR scanner. Furthermore, a patient benefits from receive coils that have improved patient comfort which is mainly determined by efficient workflow like potentially a shorter or lesser claustrophobic experience and an ergonomic design that reduces cable clutter, that adapts more flexibly to different body shapes and is more lightweight.
These issues can be addressed using a digital interface for a receive coil. In this case, analogue to digital conversion is performed already within the coil. Connector and cable size and handling issues even for high element counts in coils can be overcome by effectively combining multiple elements information to just a few optical fibers or galvanic wires.
U.S. Pat. No. 6,339,717 B1 discloses a medical examination system, particularly a magnetic resonance system comprising a host computer unit, a control computer unit and an image computer unit. Analogue to digital converters are arranged close to the radio frequency coils of the image signal reception system, where the examination system is fashioned as a magnetic resonance system.
U.S. Pat. No. 4,879,514 discloses an MRI device comprising a transmitter/receiver which, with the exception of a few components is all digital.
Digitization remote from the technical room requires the availability of the system (master) clock at the local (remote) analogue to digital converter for appropriate digital sampling, e.g. on the board of the receiver coil. This means, that the information of the master system clock has to be provided from the technical room to the receiver elements in the examination room.
US 2007/0224698 A1 discloses a magnetic resonance imaging system which is adapted for direct digitization of NMR signals.
WO 2007/043009 A2 discloses a radio frequency antenna comprising a resonant pickup circuit arranged to pick up magnetic resonance signals, and an analogue to digital converter arranged to convert the magnetic resonance signals to digital data and a frequency converter arranged to convert a primary band of frequencies of the digital data.